The name 'Elfstan' comes from Old English for 'Elf-stone', and is thus identical in meaning to Aragorn'sElvish title Elessar. He was thus presumably named for his grandfather's friend and companion (who was also High King at the time of his birth).

Elfstan would eventually succeed his father as Warden (we don't know exactly when this happened, but circumstantial evidence1 points to very roughly S.R.1520 or IV 99; if so, Elfstan would have been approaching seventy when he inherited the position). He took 'Fairbairn' as his family name and established a line that would give rise to one of the most important and influential families in the Shire: the Fairbairns of Undertowers.

Notes

1

The evidence in this case is extremely circunstantial. This dating assumes that Elfstan's father Fastred was reasonably close in age to his wife Elanor (who was known to have been born in S.R.1421) and that he had a typical Hobbit lifespan of about one hundred years.